Processor
For example, choosing a particular model of processor, you need to pay attention to the following parameters: clock frequency, number of cores and amount of cache memory (preferably to the device having a volume of not less than 12 MB). When choosing CPU, you can see that its clock frequency was not less than 2.8 GHz, but it will be more, of course, will be better. With regard to the number of cores, here it is not so, as it may seem at first glance. Not always a large number of them indicates that the computer will work quickly. Generally, the processor must be selected so that it fits in well with the video card and RAM. It's then possible to get good results. Therefore before buying it is desirable to see the table of compatible processors and a special read on the forums about this or that brand.
Video card
As for the video card, the choice of this accessory is required to be attentive to the question of compatibility with other components. Otherwise, it can not only not work, but even burn. The basic parameters that you want to pay attention to is the memory and the model itself. The amount of memory affects the performance of your PC and all software that works with graphic. As for the model, there are no special criteria. The choice of a particular model due to the games that will run on a PC, as they often can not work with one model even having the same amount of memory that is required.
RAM
Amount of RAM also affects the speed of your PC. The only thing I can say is what it will more the better, but before buying you must either consult a consultant or know myself - if a certain volume of your motherboard or not.
In addition, do not forget that the contamination of the hard disk, unnecessary programs, polluted registry can also impact on productivity, namely on a computer. Therefore, it is desirable to regularly clean your computer of unused programs and either use automated software to clean up the registry, or do it myself.